The kinesin superfamily is an extended family of related microtubule motor proteins. It can be classified into at least 8 subfamilies based on primary amino acid sequence, domain structure, velocity of movement, and cellular function. This family is exemplified by "true" kinesin, which was first isolated from the axoplasm of squid, where it is believed to play a role in anterograde axonal transport of vesicles and organelles (see, e.g., Goldstein, Annu. Rev. Genet. 27:319-351 (1993)).
Mitotic kinesins are enzymes essential for assembly and function of the mitotic spindle, but are not generally part of other microtubule structures. Mitotic kinesins play essential roles during all phases of mitosis. These enzymes are "molecular motors" that translate energy released by hydrolysis of ATP into mechanical force which drives the directional movement of cellular cargoes along microtubules. The catalytic domain sufficient for this task is a compact structure of approximately 340 amino acids. During mitosis, kinesins organize microtubules into the bipolar spindle that is the mitotic spindle. Kinesins mediate movement of chromosomes along spindle microtubules, as well as structural changes in the mitotic spindle associated with specific phases of mitosis. Experimental perturbation of mitotic kinesin function causes malformation or dysfunction of the mitotic spindle, frequently resulting in cell cycle arrest.
Within this functional group of kinesins resides a group of kinesins from several organisms that share significant sequence homology, the Kin I subfamily, and that function to destabilize microtubule ends. These include H. sapiens MCAK (also known as mitotic centromere-associated kinesin or HsMCAK), X laevis MCAK, and C. griseus MCAK.
During anaphase A, disjoined sister chromatids migrate poleward. This poleward movement is driven by kinetochores and is accompanied by the depolymerization of microtubules attached to the migrating chromatids. The kinesin MCAK plays an important role in this motility and may promote disassembly of microtubules attached to kinetochores of mitotic chromosomes.
The HsMCAK gene has a predicted 723 amino acid open reading frame, encoding a 81 kDa protein that shares 79.2% homology with hamster MCAK. HsMCAK is expressed in tissues containing dividing cells, such as thymus, testis, small intestine, colon (mucosal lining), and placenta. Genes for the Xenopus and hamster homologs of MCAK has also been cloned and characterized.
Defects in function of these proteins would be expected to result in cell cycle arrest in mitosis. As such, compounds that modulate the activity of these kinesins may affect cellular proliferation. The present invention provides a novel method to identify such compounds.